1. Field of The Invention
This invention relates to a storage medium having a readable and writable storage region (hereunder referred to as a read/write storage region) and another read-only storage region and also relates to a disk-like storage medium including a read-only storage region.
2. Description of The Related Art
In order to inexpensively provide known information or data for users, memory manufacturers develop and plan to market memories such as an optical disk of the type in which a read-only memory (ROM) region being not writable exists together with a read/write random access memory (RAM) region. Previously, an optical-disk manufacturer saves the latest information in optical disks before forwarding the optical disks by providing fundamental information (for example, information described on a map, information on layouts of stores or the like) as known information to be stored in one or more optical disks each composed of only a ROM region and writing update information for adding supplemental information to or modifying the fundamental information to one or more optical disks each composed of only a RAM region of which the stored data can be updated by users. In such a case, the information can easily be managed by containing the ROM region for storing the fundamental data and the RAM region for storing the update data in an optical disk. Moreover, efficiency in accessing and retrieving the information can be improved. Furthermore, efficiency in each user's work can be also increased.
By the way, a storage region in an optical disk is composed of a user area to be used by an user of a host system, a spare area (or preliminary area) to be used instead of a defective sector other than an initial defective sector which has already been defective at the time of forwarding the optical disk and a management area to be used for managing information to be stored in an alternate area. Further, there are the following conventional methods for managing defects in a storage medium: Sector slipping Defect Management method (hereunder abbreviated as SDM); and Linear replacement Defect Management method (hereunder abbreviated as LDM).
SDM is a method for removing a defective sector from an optical disk before a user uses the storage medium for the first time. In case of this method, logical addresses to be used for accessing the optical disk by the host system are assigned to track numbers of tracks and sector numbers of sectors physically managed in the optical disk other than defective sectors determined by Certification and spare sectors (i.e., preliminary sectors). Incidentally, Certification is an operation of detecting initial defective sectors and correcting defective areas by performing a deletion operation, a write operation and a verification operation on all storage areas of an optical disk.
LDM is a method for removing a defective sector from an optical disk when the defective sector occurs therein after SDM has been performed thereon.
Hereinafter, an example of a defect management operation effected by applying LDM to an optical disk will be described by FIGS. 12 and 13.
FIGS. 12 and 13 illustrate algorithms for managing a defect in what is called a full-RAM optical disk which is erasable and re-writable and is now under discussion in International Standardization Organization (ISO). FIG. 12 shows a state of a storage region of an optical disk on which SDM is performed.
In FIG. 12 each reference numeral (i.e., 0, 1, . . . /r 177) corresponding to a combination of a physical track number (hereunder sometimes referred to as a physical track address) and a physical sector number (hereunder sometimes referred to as a physical sector address) indicates a logical number (hereunder sometimes referred to as a logical address) assigned to a location of a storage region. For instance, a logical address 25 is indicated at and assigned to a location corresponding to the combination of a physical track address 2 and a physical sector address 1. As is seen from this figure, no logical address is assigned to a a defective sector which is represented by St. Andrew's cross x (for example, a sector indicated by the combination of a physical track address 2 and a physical sector address 2), a logical address is assigned to the next sector (namely, a logical address 26 is assigned to a sector indicated by the combination of a physical track address 2 and a physical sector address 3 which is next to this defective sector in the example).
FIG. 13 illustrates a state of an optical disk on which LDM is performed. As is shown in FIG. 13 data to be written to a sector R1 corresponding to the combination of a physical track address 5 and a physical sector address 7, which becomes defective after SDM is performed, is stored in a sector corresponding to a physical track address (hereunder sometimes referred to simply as a track address) 8 and a physical sector address (hereunder sometimes referred to simply as a sector address) 0 of a spare area together with a logical address 65. This results in that when a sector having the logical address 65 is accessed by a host computer or system, the sector indicated by the combination of the track address 8 and the sector 0 is practically accessed. Further, when an alternate sector &/r a defective sector R2 indicated by the combination of the track address 7 and the sector address 7 is allotted to a sector of a spare area, a defective sector corresponding to a track address 8 and a sector address 1 is not used as the alternate sector and a logical address 89 is assigned to the next sector corresponding to the track address 8 and the sector address 2.
Although there have been conventional defect management methods regarding what is called a full RAM, there have been proposed no suitable defect management methods regarding an optical disk of the type in which a RAM region and a ROM region coexist. The present invention is accomplished to solve such a problem of the prior art.
It is, therefore, an object of the present invention to provide a defect management method for managing a defect in a storage medium of the type in which a RAM region and a ROM region coexist.
Further, referring to FIGS. 25 and 26, there is shown a structure of an optical disk in which a RAM region and a ROM region are provided. In FIG. 25, reference numeral 2 indicating an outer hatched ring-like area represents the ROM region; and reference numeral 1 indicating an inner ring-like area designates the RAM region. FIG. 26 is a diagram for illustrating the structure of a part of a storage region of this optical disk by representing each storage cell by means of a square. As shown in this figure, the RAM region is comprised of physical tracks 0 to 7, each of which has 12 physical sectors. Further, the ROM region is composed of physical tracks 8 to 16, each of which also has 12 physical sectors.
As is seen from FIG. 26, in case of the arrangement of the ROM and RAM regions as illustrated in this figure, 7hen update information for updating the fundamental information in the ROM region is stored in the RAM region, the update information can initially be stored in physical sectors of the RAM region which are near to the ROM region. If the read-only storage region includes a code region, logical addresses are not assigned to sectors of the code region. Incidentally, in the instant application, the term "update information is defined as new information to which fundamental information stored in the ROM area is updated or changed. However, in case where a quantity of update information to be written to the RAM region is large, a part of the update information should be stored in physical sectors of the RAM region, which are far away from the ROM region. This results in that it takes time to write the update information to the RAM region and to read the update information from the RAM region.
The present invention is also created to solve such a problem of the prior art.
It is, accordingly, another object of the present invention to provide a storage medium having a RAM and ROM regions, wherein update information for updating the fundamental information stored in the ROM region is stored in a part of the RAM region, which is as near as possible to the ROM region.